First time boondocking -electricity

[HangDiver]

Originally Posted by 67L48

That furnace is drawing around 4-5 amps per hour. Running 100% for an 8-10 hour night is going to pull 40-50 amps. Even really cheap marine batteries will have around 90 Amp-hours of capacity.

You're assuming the user is starting that evening out with a fully charged battery, which is almost never the case.

[VinceU]

67L48, your assumptions are certainly light. To begin with Suburban calls for a fused 20 amp power supply. At a 25 percent overload would enable a 15 amp continuous feed, a bit more than 4-5 amps in your calculation. The other faux pas is assuming the entire battery rating is available “90 amp capacity”. The popular rule of thumb is never discharge a battery below 50% of stored value otherwise damage will result.
I like others have done it wrong, result no furnace and dead refrigerator in the morning! Lots of threads on this forum for good advice.

[HangDiver]

Rule of thumb: If you're planning to run your furnace, one battery, one night. This of course is assuming no generator to recharge.

[Jay2504]

Another thing to consider when charging the batteries with a generator. As the batteries get closer and closer to being fully charged, the slower the charge rate. The last 10percent can take longer to charge than the first 40 percent. That assumes a 50 percent drawdown over night. This is especially true for me as my WFCO converter goes to 13.6 volts and stays there with the charge amps dropping off fairly quickly. Jay

[67L48]

Originally Posted by VinceU

67L48, your assumptions are certainly light. To begin with Suburban calls for a fused 20 amp power supply. At a 25 percent overload would enable a 15 amp continuous feed, a bit more than 4-5 amps in your calculation. [...]

I'm not concerned with the fuse or power supply rating, I only care how many amps the furnace actually draws. For the furnaces in PUPs, there are typically one of two brands: Atwood or Suburban. In mine, there was an Atwood. The Atwood draws 4.2 amps. That's the number I used in my first write up with the calculations. The Suburban draws 4.6 amps. I don't know which one is in the OP's PUP. So, again, if you run this for 10 straight hours, you're going to draw between 40-50 amps off of your battery. Seems like I might have said that ..... Remember, the power to run a furnace is really just a fan motor ... it's not like you're powering up heating coils or something. So, I stand by my assumptions. So do popupportal, popupexplorer, and Google.

Originally Posted by VinceU

[...] The other faux pas is assuming the entire battery rating is available “90 amp capacity”. The popular rule of thumb is never discharge a battery below 50% of stored value otherwise damage will result. [...]

Nope, I didn't make that faux pas, either ....

Originally Posted by 67L48

[...] You should never draw a battery lower than 50% of its rating, [...]

The earlier statement made by another poster was that the battery would be near dead after a night of furnace use. Dead doesn't mean 50% left ... it means dead. As in, won't really power anything.

After a night of furnace use, the battery won't be dead. If using a cheap 90 A-Hr battery, it's not wise to continue to use it. Batteries can be damaged if discharged below 50%. But, you could continue to use it. It would still deliver plenty of amps for additional use, if you wanted. If you can still get power out of the battery, then it's not dead. Your statement above isn't actually correct. It's not a faux pas to assume the entire battery rating is available. It most certainly is ... at least once. You shouldn't, for the reasons you state, but shouldn't is different from can't.

I routinely used my furnace for three nights straight off of one battery charge. Again, it's all about knowing the power draw (4.2 A in my case) and the hours of usage. 3-5 hours a night for 3 nights ... 9-15 hours ... 40-60 amps. I need a battery 120 A-Hr to cover that use. No problem. No reasons for rules of thumb. The math is simple. Especially on a popup, the devices you're using are limited and easy to account for.

And, yes, I did assume that the user not only starts with a full charge, but that he takes care of his battery when not camping. Those might both be sketchy assumptions!

Good luck.

[rockfordroo]

Originally Posted by VinceU

67L48, your assumptions are certainly light. To begin with Suburban calls for a fused 20 amp power supply. At a 25 percent overload would enable a 15 amp continuous feed, a bit more than 4-5 amps in your calculation. The other faux pas is assuming the entire battery rating is available “90 amp capacity”. The popular rule of thumb is never discharge a battery below 50% of stored value otherwise damage will result.
I like others have done it wrong, result no furnace and dead refrigerator in the morning! Lots of threads on this forum for good advice.

Fuses are sized to protect the wiring, not the furnace. The 4-5 amps is fan's running current; the fan probably spikes to more like 10-12 amps on start up, but only for a few milliseconds; so the fuse needs to be larger than 4-5 amps to handle the starting current, but less than 20 amps to protect the wiring.

[debbiej]

I read this whole thread through, and didn't see one suggestion that has worked well for us and a lot of other people. We have a small rv as well as our pop up. we carry a 100 w solar panel, have a charge controller hooked to the batteries. our camper came with one coach battery, but we upgraded to two sealed deep cell connected together. As with most camping setups, while traveling, the vehicle charges the batteries. but when we set up for days without power, we position the solar panel in a sunny spot, plug it in to the charge controller, which is connected to the batteries and they start charging right away. our little rv has a generator on board, but I don't like the noise. the solar panel charges our batteries all day and they seldom go below a reading of 11.75 a. by morning. We have led bulbs in the lights, a danfoss generator refrigerator and use the furnace at night when it is cold and a fantastic fan when it's warm. I see many camping setups with solar panels installed on top, and that is a great idea, but we like to be able to park in the shade, so didn't want to mount it to the top.

we haven't gone camping in our pop up yet, but when we do, I'll simply hook the charge controller clamps to the battery and set up the panel in the sun. much cheaper than a generator, silent and clean.

[67L48]

debbiej,
Your experience combined with my earlier posts (that detail a typical day's worth of power draw in the 30-40 A range) is why solar panels are quite popular with PUPs and small trailers.

The questions I was addressing were specific to generator size and capability, but the same principles apply to a solar panel.

You start in the same place: what appliances and features are you using ... and for how long. You can quickly figure out how much power you're using in a day. And, again, most people in the camping season (light furnace duty) are going to be right in the 30 A range.

So, you grab a 100W solar panel that charges on a 17 V circuit. Thus, it's going to generate about 5.9 Amps (Ohm's law, again). But, you have lots of losses due to circuits, wiring, non-peak sun, etc. So, figure you lose 20% and you get around 6-hours of sun in a day. That's right around 28 Amps.

That means that, in that secenario, you're taking out ~30 Amps in a day and putting back in ~28 Amps. Not bad. You could easily do that (net consumption of ~2A per day) for a long trip without fear of damaging the battery.

I just want to address one thing you said: "the solar panel charges our batteries all day and they seldom go below a reading of 11.75 a. by morning"

I want to make sure you really mean 11.75A and not 11.75V. If you're using a Doc Wattson or similar power monitor and you mean that you seldom use more than 11.75 A, then no problem. You're using very little power.

If you mean that your batteries seldom show a reading below 11.75 V, then that's a different story, altogether. "That's a different story" (for Airplane! fans ... they still exist, right?). The voltage reading of a 12V battery isn't very intuitive. A full battery doesn't read 12.0 V. It's going to read upwards of 12.6 V. A dead battery doesn't read 0.0 V. It's going to read something in the 10 V range. If you really see 11.75 V, then you're around 30% of your battery capacity and you're damaging the battery.



Reading up over at The 12 Volt Side of Life is pretty important for any RV owner.

Good luck.

[debbiej]

when we first put the solar set up into use in our little rv, (a rialta) I read and learned what I needed to know about solar 12v systems to purchase the panel, controller and batteries. we set it all up, that was about two years ago. I do not have a good brain for things electrical, and I learned what I needed to make the solar set up work, and promptly let go of the knowledge. I could look it all up and remember the details, if need be. The charge controller reads out battery power remaining both by number with a v after it, and a little icon of a battery, which is like an idiot light on the dashboard, but it works for me! we camp a lot in the winter and run the furnace, but the fridge doesn't work as hard. In the summer, the fridge runs more. either way, we need the solar panel, vehicle engine or the generator to top off the batteries in the morning. Our batteries were bought used from a medical back up system, so could be nearing the end of life, or we could have allowed them to get too low over a period of disuse. we try to keep the rv plugged in so they stay charged, but sometimes forget. we disconnect and use a battery minder for longer periods of no being used. Our rv is a 95, so it is possible something is drawing off power as well. honestly, even though it's never broken down on us, and everything works, I'm becoming really drawn to the simplicity of pop up camping. One winter camping in canvas and I may feel differently.

[VinceU]

Yes you will feel differently, you’ll will fell cold all the time. Pop ups are not designed for all season camping, more like 6 months. When I roughed it in one with propane heater, I could easily use a bottle of propane and full battery in a weekend. No fun when one or the other empties.

[debbiej]

This is true, we have been pretty cold camping! We've had pop ups before, and a VW westfalia camper when the kids were grown. But our NM winters, though cold are usually sunny, and we don't really go into high elevations in the winter. We find a little buddy to be wonderfully warm on cold days, and usually lots of covers do the trick at night. We are camping now and it's cloudy and cold, but the furnace on this popup is hot! I prefer the gentle radiant heat of the buddy heater.